I've just caught up to the manga and I don't know if I missed this information or not, but how did Pochita end up in the state he was in at the start of the series? He looked like he had gunshot wounds.
From what I've seen, the Chainsaw Devil is very strong and I assumed that if he was killed in hell, he would end up on earth without injuries so that rules out that he was defeated by the Gun Devil in hell. Which means he was injured while on earth. Not to mention he also seems to be kinder and looks different too. So is Pochita a Fiend formed from the Chainsaw Devil taking over the corpse of a dog? And if so, could fiends make contracts with humans? I thought only devils could do that?
Sorry if this was information provided in the manga. I sometimes read this series just before going to bed so some details might have drifted away from me.